The present invention relates to hybrid vehicles. More particularly, the invention relates to an accessory drive arrangement in a hybrid vehicle.
Hybrid vehicles can include multiple drive sources, such as an internal combustion engine and an alternate drive source that is not powered by gasoline or another fossil fuel. Hybrid vehicles can achieve fuel consumption reductions by using a regenerative drive strategy in which electrical, mechanical, or hydraulic energy is stored during braking and later used to power the vehicle via the alternate drive source. Additional fuel savings can be achieved by using an start/stop strategy in which the operation of the internal combustion engine is automatically stopped and started based on driving conditions (e.g., the engine can be automatically turned off when the vehicle is cruising (i.e., not accelerating), coasting, braking, and/or comes to a stop, and subsequently automatically re-started as needed).
A variable transmission device may be used in a hybrid vehicle to provide seamless gear ratio changing for driving the wheels of the hybrid vehicle at various speeds while keeping the internal combustion engine's operating speed at a particular speed that results in maximum efficiency. One known type of variable transmission device is a serial hydraulic infinitely variable transmission (IVT), which establishes a hydraulic fluid connection in the drive train to provide seamless “shifting” between forward speed ratios, a neutral state, and reverse speed ratios. At least one known vehicle configuration utilizing a serial hydraulic IVT is described in U.S. Pat. No. 7,793,496. The U.S. Pat. No. 7,793,496 discloses various vehicle transmission configurations in which at least two hydraulic pump/motors are arranged in series along the vehicle drive train. The hydraulic pump/motors operate in various modes and speeds to modulate the speed of a driven wheel(s) somewhat independently from the operating speed of the on-board internal combustion engine.
Most conventional vehicles include a series of mechanically engine-driven accessory devices (e.g., oil pump, engine coolant pump or “water pump”, air conditioning compressor, alternator, power steering pump, brake hydraulic pump), some of which are desirable to keep running even when the internal combustion engine is turned off in the start/stop strategy. To keep such accessory devices running, the vehicle must be provided with additional drive means for driving the accessory devices at times of temporary engine stoppage, necessarily adding cost and complexity to the vehicle.